Spark Exciter Variable Control Unit

ABSTRACT

A hardware configuration and related variable control strategy is disclosed that accepts an electric power input typical of space flight systems and converts that energy into a spark pulse train with variable performance metrics for the following system parameters: time to first spark, peak breakdown voltage amplitude, spark repetition rate and energy delivered per spark, which have all been optimally chosen to reliably ignite certain fuel mixtures and which have been proven to be beneficial for use in aerospace applications.

I. CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 25 U.S.C. §119(e) of U.S. Provisional Application No. 62/339,538 filed on May 20, 2016 and of U.S. Provisional Application No. 62/339,521 filed on May 20, 2016, both of which are incorporated by reference in their entireties.

II. TECHNICAL FIELD

Provided is a spark exciter variable control unit used to determine optimal and threshold performance values required to reliably initiate combustion of flammable substances and mixtures for uses including but not limited to propulsion systems for aerospace and other applications.

III. BACKGROUND

Use of hypergolic propellants to power rockets and other space and/or aircraft is relatively common within the industry. Such propellants typically consist of a fuel (e.g., hydrazine) and an oxidizer which spontaneously ignite when they come into contact with each other. One advantage of hypergolic fuel systems are that ignition systems are not required or used for ignition and combustion of hypergolic propellants. Hypergolic fuel systems, however, can be extremely toxic and corrosive both to the propulsion system and to the environment. For this reason, the space industry is moving towards use of “green” propellants that will enable safer, more cost-effective space flight. “Green propellants” or “green fuels” are not hypergolic or toxic and offer a higher return on investment in not requiring ground support equipment and significant time for delivery and filling of fuel within the propulsion system.

The benefits of using “green” fuels within propulsion and other mechanical systems are significant in that they offer higher energy output per weight and improved ignition reliability when paired with a compatible spark exciter unit. Consequently, “green” fuels also require less storage space than that which is required for other conventional fuels.

Relative to the standard hypergolic fuels such as hydrazine, these “green” fuel mixtures are more difficult to ignite reliably and require much more energy to ignite and to burn. What is therefore needed within the industry is an improved spark exciter system which is capable of consistently initiating combustion of various types of “green” fuels.

NASA Glenn Research Center has published the results of a test of several potential spark exciter systems, and established that a spark exciter system that is capable of reliably igniting and sustaining combustion of a “green” fuel mixture of liquid oxygen and liquid methane (LO₂/LCH₄) requires approximately 200-300 sparks per second, each with 55-75 mJ of energy delivered per spark, a breakdown voltage on the order of 9-10 kV, and a deterministic and repeatable time to first spark. However, current commercially available spark exciters have not been able to consistently achieve ignition with sufficient reliability for aerospace applications.

As different “green” fuels are considered for selection as aerospace propellants, it is extremely useful to be able to test and characterize the combinations of conditions and spark exciter performance parameters that lead to reliable ignition of that specific fuel mixture. The present disclosure provides an electronic device that is capable of varying spark exciter operational parameters, including but not limited to the amount of energy delivered per spark, the spark repetition rate, and peak breakdown voltage. In an ideal test setup, the spark exciter variable control unit allows users to find the optimal spark exciter performance parameters required for reliable ignition and combustion of their system as environmental and system parameters are varied, including but not limited to fuel mixtures, fuel types, fuel flow rates, combustion chamber geometries, spark gaps/igniters, and many other factors that affect ignition and combustion in aerospace applications. The environmental parameters can be adjusted to reflect actual mission profiles and the related ignition challenges that will be faced in the end application. This can be done manually with control switches or via command control using an embedded microcontroller. The spark exciter variable control unit allows the combustion system designer/operator to quickly test their system to determine the optimal spark exciter performance parameters needed to reliably ignite their specific application across the range of environmental conditions that they expect their system to operate in. This lowers the risk of failures associated with selecting a fixed spark exciter unit that has fixed performance parameters but offers no margin information for the application that it will be operating in. That is, the unit may successfully ignite a ground test rig under certain operating conditions, but the system designer/operator would not know how close to the failure point or failure threshold level the system is operating at. For example, if 55 mJ is approximately the minimum threshold energy per spark required for reliable ignition and combustion of a propulsion system test rig at specific operating conditions, selecting a 60 mJ per spark exciter might not be sufficient to allow enough margin for other conditions that can't be tested on the ground test rig. Since the present variable control unit that can assist in determining the threshold value, one of skill in the art can proceed with additional confidence in the spark exciter performance parameters selected for the particular mission or end application. Such end applications include but are not limited to rocket propulsion systems, aircraft engines, race cars, land vehicles, systems used within the gas and oil industry, power turbines, watercraft, etc.

IV. SUMMARY

Provided is a spark exciter variable control unit and a related method implemented for reliably initiating non-hypergolic combustion of green fuels for use in space flight and other applications.

According to one aspect of the present disclosure, a spark exciter variable control unit is provided which includes an exciter assembly, an ignitor and a means for adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green, wherein the means for adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green fuels includes at least one of 1) adjusting the exciter assembly and/or ignitor with at least one remote variable potentiometer; 2) adjusting the exciter assembly and/or ignitor through a digital communication from a remote device which employs an embedded microcontroller, and 3) adjusting the exciter assembly and/or ignitor utilizing a Field Programmable Gate Array (FPGA), wherein the means for adjusting and setting of parameters is employed to determine optimal combustion performance.

According to another aspect of the present disclosure, the spark exciter variable control unit includes: (1) an input connector for receiving an electrical current; and (2) a DC-DC electrical current converter, wherein the exciter assembly and ignitor generates sparks having a voltage, energy and frequency to reliably ignite non-hypergolic fuels.

According to a further aspect of the present disclosure, the power inputs to and outputs from the spark exciter variable control unit are in a range which is suitable for space flight.

According to a further aspect of the present disclosure, the input connector function supplies an input voltage ranging from about 9 V to about 120 V and the output current may be adjusted within the range of from about 6 kV to about 25 kV.

According to a further aspect of the present disclosure, the output breakdown current supplied to a spark gap within an igniter assembly may be adjusted to about 15 kV, the spark rate may be adjusted within the range from about 1 to about 300 sparks per second and the spark energy may be adjusted between about 1 mJ to about 115 mJ.

According to a further aspect of the present disclosure, the exciter assembly includes a circuit board that receives input power from a power source, a filter to reduce conducted disturbances, a timing circuit, a power converter and a driver; the ignitor includes a capacitor, a spark plug and a spark gap; a flyback transformer is positioned between the exciter assembly and the ignitor; the flyback transformer includes a primary end and a secondary end, wherein the secondary end of the transformer is connected in series with the capacitor and the spark gap and is used to generate a breakdown voltage across the spark gap to ignite the spark plug.

According to a further aspect of the present disclosure, the timing circuit controls the operation and function of the power converter which charges the capacitor within the ignitor and the timing circuit controls the operation and function of the driver which provides an electrical power pulse to the transformer.

Also provided is a method of converting an electrical input within a spark exciter variable control unit having an input ranging from about 9V to about 120V to an output including: adjusting and setting the output to be in the range of about 6 kV to about 25 kV, wherein spark exciter variable control unit includes an exciter assembly, an ignitor and a means for adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green fuels, wherein the means for adjusting and setting of parameters is employed to determine optimal combustion performance, wherein the exciter assembly includes a circuit board that receives input power from a power source, at least one filter to reduce conducted disturbances, a timing circuit, a power converter and a driver, wherein ignitor includes a capacitor, a spark plug and a spark gap, wherein a flyback transformer is positioned between the exciter assembly and the ignitor, wherein the flyback transformer includes a primary end and a secondary end which is used to generate a breakdown voltage across a spark gap, wherein the secondary end of the transformer is connected in series with the capacitor and the spark gap wherein the timing circuit controls the operation and function of the power converter which charges the capacitor within the ignitor and wherein the timing circuit controls the operation and function of the driver which provides an electrical power pulse to the transformer, and wherein the step of adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green fuels includes at least one of 1) adjusting and setting the exciter assembly and/or ignitor with at least one remote variable potentiometer; 2) adjusting and setting the exciter assembly and/or ignitor through a digital communication from a remote device which employs an embedded microcontroller, and 3) adjusting and setting the exciter assembly and/or ignitor utilizing a Field Programmable Gate Array (FPGA), wherein the step of adjusting and setting of parameters is employed to determine optimal combustion performance.

According to a further aspect of the present disclosure, the electrical input received from the power source is passed through a filter.

According to a further aspect of the present disclosure, the electrical input is passed through the timing circuit.

According to a further aspect of the present disclosure, the timing circuit turns on a power converter which charges the capacitor within the ignitor.

According to a further aspect of the present disclosure, after the capacitor is charged by the power converter, the timing circuit initiates controlled operation of a driver.

According to a further aspect of the present disclosure, the driver sends an electrical input to the transformer which outputs an electrical current within the ignitor, wherein the transformer and capacitor are discharged in conjunction to generate the breakdown voltage across the spark gap.

According to a further aspect of the present disclosure, the timing circuit is adjustable through use of at least one associated dial.

According to a further aspect of the present disclosure, operation of the power converter is adjustable through use of a dial connected to the timing circuit, optionally, wherein the capacitor includes a storage capacity which is adjustable through use of an associated dial.

According to a further aspect of the present disclosure, operation of the driver is adjustable through use of a dial connected to the timing circuit, optionally, wherein operation of the driver is also adjustable through use of a dial directly connected to the driver.

According to a further aspect of the present disclosure, the electrical input passed through the timing circuit is adjustable through use of at least one associated microcontroller.

According to a further aspect of the present disclosure, operation of the power converter is adjustable through use of the microcontroller associated with the timing circuit, optionally, wherein the capacitor includes a storage capacity which is adjustable through use of an associated microcontroller.

According to a further aspect of the present disclosure, operation of the driver is adjustable through use of the microcontroller associated with the timing circuit.

According to a further aspect of the present disclosure, operation of the driver is further adjustable by a microcontroller associated with the driver.

V. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing several input and output capabilities/ranges of an exemplary spark exciter variable control unit, which can be utilized to determine the optimal spark exciter performance specification for specific fuels and end applications.

FIG. 2 is a system diagram showing the hardware configuration and circuit topology of an exemplary spark exciter variable control unit for igniting green propellants for space flight.

FIG. 3 is an assembly drawing of an exemplary spark exciter variable control unit.

FIGS. 4 and 5 are detailed views of the top and bottom covers of an exemplary cylindrical spark exciter variable control unit.

FIG. 6 is a detailed view of a typical cylindrical housing of an exemplary spark exciter variable control unit.

VI. DETAILED DESCRIPTION

Provided herein is a spark exciter variable control unit capable of igniting non-hypergolic fuel mixtures. The spark exciter variable control unit disclosed herein incorporates the electrical components of the exciter near the assembly which houses the igniter.

The spark exciter variable control unit disclosed herein may be used with “green” fuels. Non-limiting examples of “green” fuels which may be used within the present spark exciter system include liquid oxygen-hydrogen (LO₂/LH₂), liquid oxygen-methane (LO₂/LCH₄), nitrous oxide propane (N₂O/C₃H₈), and other liquid hydrocarbons (LO₂/hydrocarbon).

As mentioned above, these “green” fuels are more difficult to ignite and burn in a consistent manner since higher energies are required to produce higher heat for ignition and combustion. The higher energies input (including higher spark energy) establishes the reliability necessary for igniting and combusting “green” fuels. As such, an improved ignition/igniter system is needed which is capable of providing improved time to first spark repeatability, variable spark repetition rate, variable energy delivered per spark and variable maximum applied breakdown voltage. The present spark exciter variable control unit is capable of providing these functions for reliable combustion of “green” fuels in a consistent and continuous manner for the increased ignition temperatures required for initiating combustion of “green” fuels as compared to the ignition temperature of conventional fuels. The present spark exciter variable control unit accomplishes this by producing a higher energy output which is capable of not only igniting “green” fuels, but also, different combinations of “green fuels”. Also, as mentioned above, the advantage of using the present spark exciter system for combusting “green” fuels is that “green” fuels are more dense and energy potent. Thus, less space is needed to store “green” fuels within the vehicle or other mechanical device for operation than that which would be needed to store conventional fuels which would provide an equivalent amount of power.

The present spark exciter variable control unit achieves this objective through the use of a control strategy (also referred to herein as a “control system”) integrated within the spark exciter electronics design. An example of a previous spark exciter electronics design is disclosed within U.S. Pat. No. 8,653,693 which is herein incorporated by reference in its entirety. The components of the present spark exciter which allow for the implementation of the control strategy include a power source, an electronic filter, a driver (also referred to herein as a “driver circuit”, a timing sequence (also referred to herein as a “timing circuit”), a power converter, a flyback transformer, an energy storage capacitor, and an igniter (for example, a spark plug). The electrical components may be integrated within a single or multiple electrical boards. In certain embodiments, the electronic components are integrated within a single electrical board. To allow for the variable control of the parameters listed previously, additional inputs/interfaces are available at the timing circuit that allow remote control of the spark exciter performance parameters. In certain embodiments, the electronic components are integrated into a stainless steel hermetic enclosure which is operated within a vacuum environment. The unit is compact in nature and efficiently transfers energy to a given spark gap. The unit is designed to provide a fixed frequency spark rate with controlled spark energies and is designed to NASA supplied specifications for space operation of flight systems.

Referring to FIG. 2, the spark exciter variable control unit embodiment (10) includes an exciter assembly (12) and an igniter (14). An example of an igniter may be a spark plug although it should be understood that any type of igniter or spark plug may be used with the unit. The embodiment of the exciter assembly (12) shown (also referred to herein as the “electronic assembly”) includes a circuit board that first receives input power from a power source (16), filters the power which is received to reduce conducted disturbances, and powers several downstream circuits. The exciter (12) also includes a timing circuit (20). The timing circuit (20) runs a power converter (22). The timing circuit (20) also controls the operation of a driver (26) which is used to provide an electrical power pulse to a transformer (28). The timing circuit allows for the variable spark exciter performance parameters to be selected by the user. One embodiment utilizes remote variable potentiometers to adjust the performance parameters mentioned earlier. Other methods for variation of these spark exciter performance parameters include but are not limited to digital communications with remote devices using an embedded microcontroller, Field Programmable Gate Array (FPGA), or similar hardware. Parameters can be adjusted one at a time, several at a time, or via a small script that could be performed by the spark exciter variable control unit. That is, each spark could be defined individually, meaning that each subsequent spark energy could be increased by 1 mJ, etc. In certain cases, ignition reliability can be improved by initially generating high spark energies, high spark rates and high peak breakdown voltages. However, these operating metrics do not need to be sustained shortly after ignition as combustion continues. Consequently, there can be a dynamic reduction of spark exciter performance specifications after ignition.

The transformer includes a primary and a secondary winding which is used to generate the breakdown voltage across the spark gap. The secondary end of the transformer (28) is connected in series with the energy storage capacitor (24) and the spark gap. The energy storage capacitor (24) is connected across and charged by the power converter (22). Varying the power converter output voltage, which is equal to the voltage across the capacitor, sets the stored energy value that will ultimately be delivered to the spark gap over the duration of the spark event. The greater the capacitor voltage, the greater the amount of stored spark energy. During operation, the exciter driver circuit (26) sends a voltage pulse to the primary of the flyback transformer (28). When the driver pulse is terminated, the magnetic field in the transformer core rapidly decreases and voltages related to the turns number are generated across the primary and secondary windings. By varying the duration of the primary pulse, the amount of energy stored in the transformer core gap is varied. This energy is related to the flyback energy available and the related peak flyback voltages, which in this case is the peak breakdown voltage level. The series connection of the capacitor (24) and transformer (28) secondary causes the sum of the voltages to appear across the gap. This generates a high voltage pulse that is sufficient to cause breakdown to occur across the gap and an arc or plasma to be generated. The low impedance plasma effectively closes the gap and creates a current loop path that allows the energy storage capacitor to discharge through the secondary of the transformer, transferring the capacitor energy to the spark gap and initiating the ignition process. Repeated spark generation and ignition of the air/fuel mixture ensures that combustion is maintained throughout the engines operation. Varying the spark rate ensures a greater probability of ignition success due to the fact that one failed ignition event will be followed up shortly after by another attempt. Most systems typically don't want to wait too long before the next spark because unburned fuels could be building up and creating a potentially hazardous situation. This is the reason why high spark rates can be beneficial to ignition reliability and also the same reason why a deterministic and relatively quick time to first spark may be advantageous.

The spark exciter assembly may be integrated with the igniter within a single assembly or enclosure or alternatively, the exciter assembly and the igniter may consist of two separate electrically connected components. The exciter assembly may be designed in any shape required for a particular application. In certain embodiments, the exciter assembly may be designed to be rectangular in shape. Although the positioning and design of the various components of the exciter assembly as well as the igniter have been described above, it is understood that a person of ordinary skill in the art may develop alternative designs of the exciter and igniter units and may position the various components described above anywhere with respect to the circuit board depending upon any specifications that may be required for a particular application.

In the end application, the power input for the spark exciter originates from a power source from a vehicle or other electrical equipment. The power source may stem from a battery, an alternator, a generator or any other power source suitable for use within the art. In certain embodiments, the power input may be a direct current (DC) input originating from a DC power source. The power source may be run at any voltage suitable for use within the art. In certain embodiments, the power source may be run between about 9 to about 50 volts. In further embodiments, the power source may be run between about 24 and about 32 volts (28 Vdc nominal).

The present exciter system shown in FIG. 2 is run from a DC power source. However, the exciter system of the present disclosure also encompasses designs capable of accepting an alternating current (AC) power input which originates from an AC power source. Thus, in certain embodiments, the power source may also be generated from an AC power source.

After electrical power is received from a source within the exciter assembly (12), it is passed through a filter (18) to reduce conducted disturbances. The filter may encompass any component suitable for use within the art as a filter. Examples of component devices which may be used as filters include but are not limited to inductors, capacitors, diodes, current limiters, inrush current limiters, resistors and combinations thereof.

After current passes through the filter it is run to the driver circuit (26), the timing circuit (20) and the power converter (22). The timing sequence circuit controls the operation/function of the transformer driver and the power converter circuits. The power converter is first turned on to charge the capacitor, then the power converter is shut down. The driver circuit then sends a pulse to the transformer to initiate the fly-back voltage that causes a high voltage pulse and breakdown at the spark gap location. The stored capacitor energy is then dissipated at the spark gap until it is depleted. The process includes some additional delays as needed, but this pattern will repeat as long as power is applied to the spark exciter unit.

As shown in the block diagram of FIG. 1, the spark exciter variable control unit of the present disclosure may have an input of about 9V to about 120V and an output breakdown voltage of about 6 kV to about 25 kV. Spark rate may range from about 1 to about 300 sparks per second and spark energy may range from about 1 millijoule (mJ) to about 115 mJ.

The present exciter assembly may be used to break down the gap of any igniter (e.g., any spark plug). It also provides a control strategy which is reliable in that it works repeatedly to produce relatively hot plasma compared to conventional igniter systems and sustains ignition rates of a specific number of sparks per second. In certain embodiments, the spark exciter is specifically designed for incorporation and operation of flight systems. In certain embodiments, the spark exciter is designed for use in propulsion systems for space craft. In such embodiments, the spark exciter may encompass an exciter electronic assembly which is directly mounted on a flight-qualified igniter. The spark exciter may therefore comprise a compact single unit to reduce ignition system complexity. As a single unit, the spark exciter eliminates the use of a corona-prone ignition cable to produce reliable sparks for ignition of “green” fuels such as liquid oxygen, liquid methane fuels (LO₂/LCH₄) or other LO₂/hydrocarbons. The spark exciter is capable of producing 50 to 120 millijoule of energy per spark at a rate of about 100 to about 300 sparks per second through the generation of a spark gap breakdown of up to about 18 kilovolts. In certain embodiments, the spark exciter may have the following parameter values or equivalents thereof—spark rate: 100 Hz; voltage input 24-32 VDC; peak spark potential 15 kV; and delivered energy 70 mJ.

The present exciter assembly may be set to accommodate the continuous ignition and combustion any type of “green” fuel that is being used within the system. This is accomplished by setting the energy level per spark and the spark rate generated by the exciter assembly. By setting these parameters within the exciter assembly, the exciter assembly can generate the peak voltage for breaking down the spark gap which is required to ignite the particular “green” fuel that is to be burned. In one embodiment of the present disclosure, the output voltage is about 15 kV, the spark rate is about 100 Hz, and the delivered energy is about 70 mJ. In another embodiment of the present disclosure, the output voltage is about 15 kV, the spark rate is about 260 Hz, and the spark energy is about 50 mJ. In another embodiment of the present disclosure, the output voltage is about 15 kV, the spark rate is about 110 Hz, and the spark energy is about 105 mJ. In another embodiment of the present disclosure, the output voltage is about 15 kV, the spark rate is in the range of about 11 to about 100 Hz, and the spark energy is in the range of about 12 to about 100 mJ. In another embodiment of the present disclosure, the output voltage is in the range of 0.1 kV to 18 kV, the spark rate is in the range about 11 to about 100 Hz, and the spark energy is in the range about 12 to about 100 mJ.

FIGS. 3 through 6 are technical drawings of an exemplary spark exciter variable control unit which illustrates a typical cylindrical unit assembly with associated detail drawings showing how a typical housing unit could fit together.

In certain embodiments, the capacitor is capable of storing about 300V although the storage capacity of the capacitor may vary depending on the type of capacitor used within the spark exciter system and the ignition and combustion requirements for the particular fuel that is being used. Once the electrical current is discharged from the transformer, it is combined with the current discharged from the capacitor to bridge the spark gap. Thus, in one embodiment described herein, about 15,000V originating from the transformer is combined with about 300V originating from the capacitor to fill the spark gap (30). This current will cause the spark gap (30) to arc and break down plasma to generate. The plasma will function as a conductor, closing the loop within the circuit. As current flows through the spark gap (30), the plasma and high temperature is maintained across the gap causing combustion of the air/fuel mixture. After the spark is generated, there is a delay. In certain embodiments, the timing circuit may wait beyond the amount of time for the spark to end before it starts the process of respectively powering the capacitor and transformer again through the power converter and the driver. This process is repeated to provide continuous reliable ignition and combustion of the air/fuel mixture.

Through the timing circuit, the exciter assembly is able to provide variable spark rate capable of igniting and combusting “green” fuels. Typically the timing circuit allows the spark rate to be set anywhere from between about 1 to about 300 sparks per second. In certain embodiments, spark rate may be set to about 200 sparks per second while in other embodiments spark rate may range from about 1 to 110 sparks per second. The timing circuit and overall exciter system, however, may be set to generate any spark rate which is required for ignition and combustion of the specific “green” fuel being utilized within the system.

Thus, the timing of the spark rate is driven by the hardware of the exciter assembly (12) which includes the timing circuit, the driver, the power converter, the transformer and the capacitor. In general, these components within exciter assembly (12) include numerous resistors and capacitors which run the timing of the spark or ignition within the igniter. In particular, the timing circuit (20) includes various resistors and capacitors which first powers the power converter (22) to initiate the filling of an electrical potential within the capacitor (24), turns the power converter (22) off, initiates a brief delay and subsequently powers the driver (26) which in turn powers the transformer. A brief delay is introduced into the system as the capacitor (24) is discharged and the spark gap is broken down. The timing circuit (20) then reinitiates current flow to the power converter (22) to recharge the capacitor (24) and repeat the process over again. Thus, the system may be described as an analog electronic system which incorporates the use of a resistor-capacitor circuit. Time delays and constellations between the different components within the system are based on an RC time constant between the different components within the system. Briefly, the operation of components of the exciter assembly (12) as well as the timing circuit (20) can be described as follows. A first component within the exciter assembly (12) or timing circuit (20) will run for certain period of time and will initiate operation of the next component downstream from the first component. Once operation of the first component is complete, the second component will run for a certain period of time and initiate operation of the next component downstream from the first component. This process continues until operation of all the components within the cycle are completed. Once the cycle is complete, the circuit resets to begin the process over again.

The present exciter assembly may be adjusted and set to accommodate the continuous ignition and combustion any type of “green” fuel that is being used within the system. This is accomplished by adjusting the energy level per spark and the spark rate generated by the exciter assembly to determine the ignition and combustion settings for the particular fuel being utilized and by setting the ground test unit according. By determining, adjusting and setting these parameters within the exciter assembly, the exciter assembly can generate the peak voltage for breaking down the spark gap which is required to ignite the particular “green” fuel that is to be burned. In one embodiment of the present disclosure, the output voltage may be adjusted to about 15 kV, the spark rate to about 100 Hz, and the delivered energy to about 70 mJ. In another embodiment of the present disclosure, the output voltage may be adjusted to about 15 kV, the spark rate to about 260 Hz, and the spark energy to about 50 mJ. In another embodiment of the present disclosure, the output voltage may be adjusted to about 15 kV, the spark rate to about 110 Hz, and the spark energy to about 105 mJ. In another embodiment of the present disclosure, the output voltage may be adjusted to about 15 kV, the spark rate may be adjusted to be in the range of about 11 to about 100 Hz, and the spark energy may be adjusted to be in the range of about 12 to about 100 mJ. In another preferred embodiment of the present disclosure, the output voltage may be adjusted to be in the range of 0.1 kV to 18 kV, the spark rate may be adjusted to be in the range about 11 to about 100 Hz, and the spark energy may be adjusted to be in the range about 12 to about 100 mJ.

Accordingly, the ground test unit may be described as a variable system wherein the energy level per spark, the spark rate and the peak voltage that is used to break down the spark gap can be adjusted and changed to meet the ignition and combustion requirements of the fuel being utilized. In certain embodiments, the spark exciter ground test unit is an analog system wherein dials are used to control the spark rate, output voltage and delivered energy. In certain embodiments, the spark exciter ground test unit includes at least three dials to control spark rate, output voltage and delivered energy. In operation, turning the dial adjusts a resistor or potentiometer that adjusts the spark rate and spark energy through a dial. With respect to the capacitor, a dial may be used to change the output voltage of the power converter to change the energy stored in the capacitor to a higher or lower voltage within the spark loop. In summary, the spark exciter ground test unit may be adjusted with a potentiometer or resistor through the use of a dial which may be connected to various components within the exciter system including the timing circuit, power converter, capacitor, driver and transformer. In other embodiments, the spark exciter ground test unit may include a microcontroller or computer system which is used to adjust the various ignition and combustion parameters or variables described above. In such embodiments, one or more microcontrollers may be connected to various components within the exciter system including the timing circuit, power converter, capacitor, driver and transformer. In further embodiments, the spark exciter ground test unit also includes an interface which is used to adjust or change the ignition and combustion parameters or variables described above. Thus, the spark exciter ground test unit may change the ignition and combustion parameters mechanically, manually or electronically.

While the spark exciter variable control unit and corresponding methods have been described above in connection with various illustrative embodiments, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function disclosed herein without deviating therefrom. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments may be combined or subtracted to provide the desired characteristics. Variations can be made by one having ordinary skill in the art without departing from the spirit and scope hereof. Therefore, the spark exciter variable control unit should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitations of the appended claims. 

What is claimed is: 1) A spark exciter variable control unit comprising an exciter assembly, an ignitor and a means for adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green, wherein the means for adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green fuels comprises at least one of 1) adjusting the exciter assembly and/or ignitor with at least one remote variable potentiometer; 2) adjusting the exciter assembly and/or ignitor through a digital communication from a remote device which employs an embedded microcontroller, and 3) adjusting the exciter assembly and/or ignitor utilizing a Field Programmable Gate Array (FPGA), wherein the means for adjusting and setting of parameters is employed to determine optimal combustion performance. 2) The spark exciter variable control unit of claim 1, wherein the spark exciter variable control unit comprises: (1) an input connector for receiving an electrical current; and a (2) a DC-DC electrical current converter; wherein the exciter assembly and ignitor generates sparks having a voltage, energy and frequency to reliably ignite non-hypergolic fuels. 3) The spark exciter variable control unit of claim 2, wherein the power inputs to and outputs from the spark exciter variable control unit are in a range which is suitable for space flight. 4) The spark exciter variable control unit of claim 3, wherein the input connector function supplies an input voltage ranging from about 9 V to about 120 V and wherein the output current may be adjusted within the range of from about 6 kV to about 25 kV. 5) The spark exciter variable control unit of claim 4, wherein the output breakdown current supplied to a spark gap within an igniter assembly may be adjusted to about 15 kV, wherein the spark rate may be adjusted within the range from about 1 to about 300 sparks per second and wherein the spark energy may be adjusted between about 1 mJ to about 115 mJ. 6) The spark exciter variable control unit of claim 5, wherein the exciter assembly comprises a circuit board that receives input power from a power source, a filter to reduce conducted disturbances, a timing circuit, a power converter and a driver, wherein ignitor comprises a capacitor, a spark plug and a spark gap, wherein a flyback transformer is positioned between the exciter assembly and the ignitor, wherein the flyback transformer comprises a primary end and a secondary end, wherein the secondary end of the transformer is connected in series with the capacitor and the spark gap and is used to generate a breakdown voltage across the spark gap to ignite the spark plug. 7) The spark exciter variable control unit of claim 6, wherein the timing circuit controls the operation and function of the power converter which charges the capacitor within the ignitor and wherein the timing circuit controls the operation and function of the driver which provides an electrical power pulse to the transformer. 8) A method of converting an electrical input within a spark exciter variable control unit having an input ranging from about 9V to about 120V to an output comprising: adjusting and setting the output to be in the range of about 6 kV to about 25 kV, wherein spark exciter variable control unit comprises an exciter assembly, an ignitor and a means for adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green fuels, wherein the means for adjusting and setting of parameters is employed to determine optimal combustion performance, wherein the exciter assembly comprises a circuit board that receives input power from a power source, at least one filter to reduce conducted disturbances, a timing circuit, a power converter and a driver, wherein ignitor comprises a capacitor, a spark plug and a spark gap, wherein a flyback transformer is positioned between the exciter assembly and the ignitor, wherein the flyback transformer comprises a primary end and a secondary end which is used to generate a breakdown voltage across a spark gap, wherein the secondary end of the transformer is connected in series with the capacitor and the spark gap, wherein the timing circuit controls the operation and function of the power converter which charges the capacitor within the ignitor and wherein the timing circuit controls the operation and function of the driver which provides an electrical power pulse to the transformer, and wherein the step of adjusting and setting parameters required for reliably initiating ignition and combustion of non-hypergolic green fuels includes at least one of 1) adjusting and setting the exciter assembly and/or ignitor with at least one remote variable potentiometer; 2) adjusting and setting the exciter assembly and/or ignitor through a digital communication from a remote device which employs an embedded microcontroller, and 3) adjusting and setting the exciter assembly and/or ignitor utilizing a Field Programmable Gate Array (FPGA), wherein the step of adjusting and setting of parameters is employed to determine optimal combustion performance. 9) The method of claim 8, wherein the electrical input received from the power source is passed through a filter. 10) The method of claim 9, wherein the electrical input is passed through the timing circuit. 11) The method of claim 10, wherein the timing circuit turns on a power converter which charges the capacitor within the ignitor. 12) The method of claim 11, wherein after the capacitor is charged by the power converter, the timing circuit initiates controlled operation of a driver. 13) The method of claim 12, wherein the driver sends an electrical input to the transformer which outputs an electrical current within the ignitor, wherein the transformer and capacitor are discharged in conjunction to generate the breakdown voltage across the spark gap. 14) The method of claim 13, wherein the timing circuit is adjustable through use of at least one associated dial. 15) The method of claim 14, wherein operation of the power converter is adjustable through use of a dial connected to the timing circuit, optionally, wherein the capacitor comprises a storage capacity which is adjustable through use of an associated dial. 16) The method of claim 14, wherein operation of the driver is adjustable through use of a dial connected to the timing circuit, optionally, wherein operation of the driver is also adjustable through use of a dial directly connected to the driver. 17) The method of claim 13, wherein the electrical input passed through the timing circuit is adjustable through use of at least one associated microcontroller. 18) The method of claim 17, wherein operation of the power converter is adjustable through use of the microcontroller associated with the timing circuit, optionally, wherein the capacitor comprises a storage capacity which is adjustable through use of an associated microcontroller. 19) The method of claim 17, wherein operation of the driver is adjustable through use of the microcontroller associated with the timing circuit. 20) The method of claim 19, wherein operation of the driver is further adjustable by a microcontroller associated with the driver. 